The International Samba syllabus has just one version -- the left foot version you see above. However, some American style Samba syllabi include a RF version. The most likely reason: There's no Natural Basic in any American style Samba syllabus. American style dancers with no International exposure are not accustomed to dancing a Samba Box with RF forward and LF back. If you are used to a Samba Basic that begins forward on the left foot, then it's much more natural to start with your LF forward on 1, and follow with a RF Corta Jaca action on the 2&3&4&.